In previous patent applications, now U.S. Pat. Nos. 4,052,648 and 4,266,177, the applicant described power control systems for induction motors wherein the phase angle between current and voltage, or power factor, was controlled. In those systems, there were two features which were, to an extent, objectionable. One was that in order to determine the phase angle of motor current with respect to motor voltage, a resistor had to be placed in the current path to the motor, and this, in addition to creating a power loss, was inconvenient in that different sized resistors were required for different sized motors. The second objectionable features was that while the greatest improvement in power savings was achieved with a maximum value of selected power factor, this reduced the capability of a motor to adequately respond to suddenly applied loads.
It is the object of this invention to overcome both of these difficulties.